This invention relates to a formation method and device for curved plates.
Generally, two methods are being widely used in forming ship hull pieces: hot forming and cold forming. Since mechanical cold forming can be easily controlled using a press or a roller, it is mainly used as a method to form slightly curved plates or simple plates with constant curvature overall their area and as a preceding method for forming doubly curved plates. Hot forming method, which uses residual thermal elastic-plastic deformation to be caused in heating, is mainly used as a second method to form doubly curved plates or a method to remove residual welding deformation in ship blocks.
The hot forming method has been called a line-heating process as plates are heated in a constant direction. This line-heating process needs a lot of forming information such as heating positions, heating speed, cooling positions, cooling speed, etc. In the former process, skillful workers have decided this forming information. Worse, some technical systems and databases have not yet been built in relation with this process.
To simulate mechanism of line-heating process and to systematically provide forming information, some 3-dimensional thermal elastic-plastic analyses have been studied and published. However, such methods are not adequate and practical in production shops due to extensive calculations and time.
Some researchers have been conducted to improve this defect. They are roughly divided into two categories. One category is to derive a simple formula from the relationship between heat input and the corresponding residual deformation, which is obtained from experimental data. This has advantages in reducing time when compared with the thermal elastic-plastic analysis. The other category is to use a simple model in the thermal elastic-plastic analysis. Recently, some models with a simplified analysis to improve an initial beam model have been developed; including a 2-dimensional strip model, a 2-dimensional elastic-plastic theory for a round plate under spring constraint, and a modified strip model. This approach has some difficulties in assuming the accurate structural behavior and consuming much time in practically simulating the line-heating process.
Moreover, simplified formula and simplified analyses have fatal faults in offering exact forming information since shrinkage. In other words, the in-plane strain is not taken into consideration, even though the arbitrary curved plates have both in-plane strains and bending strains that are indispensably yielded in the forming process. If only bending strains are considered in generating the forming information, the basic errors cannot be resolved.
Formerly, forming information has been also obtained only from the relationship between flat plates and their objective curved plates. The objective curved plates are formed through some stages. Such former methods have not considered these stages to again form the plates which are partially formed into the objective curved plates. As a result, the practical line heating process cannot be realized.
Though forming information was obtained on basis of an inaccurate theory or was generated by intuition of the skillful workers, a systematic database has not been built relating to such forming information. An information model must be examined on this manufacturing process as closely as possible. However, such information model has not been investigated until now. Consequently, little data is known and has never been used.
Conclusively, in former techniques for the formation of curved plates, forming information depends on workers"" experiences, and is subject to errors due to its inaccurate bases, and its flow has not been examined and its manipulation has not been systematic. That is, there is no known technique used to obtain computerized and structured data from the existing forming information.
In this invention, it is intended to improve the productivity in shipbuilding and automate a formation process of curved plates, specially, a line-heating process by establishing a new forming process to make better curved plates in which inexact forming information is used only considering bending strain and developing some techniques corresponding to this process. Such techniques are divided into two methods: one is a component technique to yield accurate forming information and the other is a system technique to utilize the information efficiently.
This invention is intended to provide workers with accurate forming information and to form curved plates more close to their objectives specially in the hot forming process, e.g., line-heating in which curved plates are formed by locally heating one side of plates with a torch. Moreover, this invention automates the forming process. Such purposes are accomplished by constructing a database on various data and forming information systematically, which are previously obtained by workers through experiences, by inferring new information from this database through the artificial neural network method, and by calculating in-plane and bending strains from relationship between initial flat plates or any initially-curved plates and their objective plates.
This invention adopts three main component techniques to obtain accurate forming information. One is to calculate in-plane and bending strains. Another is to simulate the formation process of curved plates by developing a numerical mode. And the third is to calculate and infer the forming information.
To efficiently utilize forming information produced through these three techniques in practical manufacturing, this invention includes the following techniques:
to computerize the formation process of ship hull pieces systematically,
to establish its product model on a basis of the object-oriented concept to integrate various data,
to build a product database on a basis of this product model, and
to provide new information to form the plates which is partially formed into their objective curved plates. This new information helps plates to converge to their objectives.
According to one aspect of this invention, there is provided a ship hull-piece forming method comprising the steps of: (a) constructing a product database by using a relational database management system and by building product model on a basis of information modeling about formation data and processes; (b) measuring the shape of a plate and processing data; (c) performing numerical analyses on a basis of thermal elastic-plastic theory, which have forming information on the above measured plate and information on heating position as an off-line training or programming; (d) inferring forming information that is applied to new plates with multiplayer artificial neural network from the product database which includes data obtained by numerical simulations and measured in the previous works; and (e) generating information on heating paths and heat condition by calculating in-plane and bending strains from relationship between flat plates and the objective curved plates and from relationship between the objectives and plates partially formed in the middle of formation; wherein the difference between any shaped plate partially formed in the middle of formation and their objective plates can be measured during the process and the in-plane and bending strains can be numerically calculated based on that difference to provide the forming information; and wherein the formation step is completed by repeatedly making this measurement and calculation at each processing step.
According to another aspect of this invention, there is provided the ship hull-piece forming method having abilities of offering forming information to workers through monitors and worksheets, sending the forming information to the automatic device for line-heating process, and storing intermediate forming information from this device to the product database.
According to another aspect of this invention, the information-generating step (e) has abilities of providing heating paths for the transverse formation, which are determined perpendicularly to maximize principal directions of bending strains by calculating the ratio between maximum principal bending strains and minimum ones, and providing heating paths for the longitudinal formation, which are determined perpendicularly to maximum principal directions of in-plane strains by calculating the ratio between maximum principal in-plane strains and minimum ones.
According to another aspect of this invention, the numerical analysis step (c) comprises steps of (c-1) setting up parameters such as sizes of plates, initial curvature of plates, speed of a torch, the clearance between a torch and a cooler, film coefficient, the number of finite elements; (c-2) setting up material properties like condition coefficient and specific heat quality, to model a heat source and a cooling method, calculating temperature distribution in each time step, and making post-process to show the calculating results effectively; and (c-3) setting up material properties like conduction coefficient, elastic coefficient, thermal expansion coefficient, yield stress, determining boundary conditions, calculating strains and stresses with temperature distribution, and making post-processing to effectively show calculating results.
According to another aspect of this invention, the database-construction step (a) has a relational product database and having steps of (a-1) information modeling containing the flow of data in formation process of ship hull-pieces on a basis of the object-oriented concept; (a-2) definition of product model about formation process of ship hull-piece on a basis of the object-oriented concept, in which product model data cover all information over total life cyclexe2x80x94design, production and wastexe2x80x94of specific product such as phase 1, phase 2, phase 3, and phase 4 wherein the phase 1 is the selection of objects that is Hull piece and kinematics, Bending strain and in-plane strain, Principal curvature and piece forming method, Rolling and rolling condition, Line-heating and heating condition, Material property and NURBS surface, Offset table and surface measuring, Measuring points and measuring sequence, Heating line set and heating sequence, and Communication method and ANN model, the phase 2 is the definition of their attributes and their relationship, the phase 3 is the setup of their constraints, and the phase 4 is the model integration of these objects; and (a-3) construction of the product database which some forming information is saved to and retrieved from on a basis of such product model.
According to another aspect of this invention, there is provided an information-generation system for ship hull-piece formation comprising a measurement module in which the shape of plates in process and forming information is measured with some devices; a numerical analysis module in which heating conditions are calculated and verified, and this process is simulated, using a numerical program for thermal elastic-plastic analysis; a display module in which information is displayed in a monitor of a personal computer (PC) and is printed out through a printer; a data access module in which measuring and forming information is stored to and retrieved from a product database and a STEP physical file that has measuring and forming information is available; an inference module in which forming information and heating conditions about a plate to newly form are predicted from data of the product database by an artificial neural network method; an information-generating and control module in which each module previously described is controlled by a program of this module and forming information is obtained through calculation of in-plane and bending strains in the processing stages, wherein heating paths or locations to heat on are determined, comparing in-plane strains and bending strains with each other; a communication module through which the information-generating and control module transmits forming information, heating conditions and heating paths to numerical control machine based on PC (PC/NC) and through which the measured and the formation results are transmitted and stored to the product database.